All-perovskite tandem solar cells (TSCs), composed of a wide-bandgap (WBG, 1.7-1.8 eV) top cell and a narrow-bandgap (NBG, 1.2-1.3 eV) bottom cell, are regarded as a promising approach to surpass the Shockley-Queisser (SQ) limit of single-junction perovskite solar cells (PSCs). With rapid advancements in sub-cells and interconnecting layers, TSCs have achieved a certified power conversion efficiency (PCE) of 30.1%, showcasing significant commercial potential as a cost-effective photovoltaic (PV) technology. However, the interface contact between NiOx and self-assembled monolayers (SAMs) in the WBG sub-cell has constrained the efficiency and stability of TSCs. In conventional strong-acidic phosphoric acid-based SAMs (PA-SAMs), the anchoring of phosphoric acid (PA) corrodes the active NiOx layer, compromising device stability. Additionally, SAM aggregation leads to interface losses and open-circuit voltage (VOC) deficiencies.
To address these challenges, researchers Ziyi Ge and Chang Liu from the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, developed an innovative strategy based on prior perovskite solar cell research. This approach reduces the corrosion of the NiOx active layer by the SAM layer while enhancing device efficiency and stability.
The team employed boric acid (BA) as a milder anchoring group, adsorbed onto NiOx through strong –BO₂⁻–Ni coordination. Benzothiophene groups strengthen the interface bond via S-Ni orbital interactions, generating higher binding energy than PA-SAMs. This design promotes uniform SAM formation. Leveraging this strategy, the team achieved a PCE of 20.1% for the WBG cell. When integrated with an NBG sub-cell, the two-terminal TSCs’ PCE reached 28.5%, retaining 90% of their initial PCE after 500 hours of maximum power point tracking under 1-sun illumination. This research significantly advances the development of high-performance tandem solar cells, accelerating the commercialization of this advanced PV technology.
